Re: compaction: trying to understand the code

[Wu Fengguang <fengguang.wu@intel.com>]

On Wed, Aug 18, 2010 at 05:19:21PM +0900, Iram Shahzad wrote:
> >>In other words, what is it that is supposed to increase the "inactive"
> >>or decrease the "isolated" so that isolated > inactive becomes false?
> >>
> >
> >See places that update the NR_ISOLATED_ANON and NR_ISOLATED_FILE
> >counters.
> 
> Many thanks for the advice.
> So far as I understand, to come out of the loop, somehow NR_ISOLATED_*
> has to be decremented. And the code that decrements it is called here:
> mm/migrate.c migrate_pages() -> unmap_and_move()
> 
> In compaction.c, migrate_pages() is called only after returning from
> isolate_migratepages().
> So if it is looping inside isolate_migratepages() function, migrate_pages()
> will not be called and hence there is no chance for NR_ISOLATED_*
> to be decremented. Am I wrong?

The loop should be waiting for the _other_ processes (doing direct
reclaims) to proceed.  When there are _lots of_ ongoing page
allocations/reclaims, it makes sense to wait for them to calm down a bit?

Thanks,
Fengguang

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